The frequency of external symptoms of barotrauma varied among species. Other studies have seen diverse species responding to barotrauma differently as well (Hannah et al., 2007; Hannah et al., 2011; Hannah and Matteson, 2007; Jarvis and Lowe, 2008; Pribyl et al., 201l, Rodgveller et al., 2017). Symptoms of barotrauma in Canary Rockfish were similar in other studies, where the most common symptoms were EX and EET (Pribyl et al., 2011; Hannah et al., 2008). Blue and Deacon Rockfish expressed different rates for all barotrauma symptoms, even though they are phylogenetically related (Frable et al., 2015). This suggests that life history and phylogenetic relatedness do not always accurately predict how rockfish will respond to barotrauma (Pribyl et al., 2011). When I combined data from all species, the capture depth was related to frequency of barotrauma. When I separated the species, barotrauma was positively correlated with depth in only Blue Rockfish and Gopher Rockfish (Figure 3; Figure 4; Table 4). The presence of macroscopic barotrauma signs was positively correlated to capture depth in other studies as well (Pribyl et al., 2011; Jarvis and Lowe, 2008; Curtis et al., 2015). However, this relationship was not observed in Canary Rockfish or Deacon Rockfish (Table 4). Other studies also did not observe this correlation in Canary Rockfish (Hannah and Matteson, 2007; Pribyl et al., 2011). It is interesting that Blue Rockfish and Deacon Rockfish did not display similar results in relation to depth of capture and expressions of barotrauma since they are sister species. I think the depth range sampled was too narrow to observe this trend in Deacon Rockfish. Hannah et al., 2008 found that external signs of barotrauma increased in frequency with capture in Deacon Rockfish.
However, their depth ranges were between 10-51 meters (Hannah et al., 2008), whereas most Deacon Rockfish sampled in my study were between 25-35 m, (Table 3). Therefore, it appears capture depth does influence frequency of barotrauma, but deeper depths may need to be sampled to see this correlation in some species.
Canary Rockfish were more likely to have barotrauma when experiencing a greater temperature change from the bottom to the surface. The average temperature difference between the bottom and surface temperature was 2C. Other studies have shown that larger temperature differences increase the incidence of barotrauma in Pacific rockfishes (Jarvis and Lowe 2008; Hannah et al., 2011). Gases expand more in warmer temperatures, which may lead to a higher susceptibility to barotrauma (Pribyl et al., 2009). Therefore, barotrauma injuries could be more severe in areas with strong
thermoclines. Increased temperature differentials between capture depth and the surface may also increase discard mortality (Davis, 2002). Canary Rockfish may have been the only species to show a correlation between temperature difference and barotrauma because they were caught at deeper depths with colder temperatures. Therefore, Canary Rockfish experienced the largest temperature change compared to the other species.
The size of the fish did not affect the presence of barotrauma or immediate behavior after recompression in my study. Other studies have not seen a correlation between fish size and incidents of barotrauma or on short-term survive after
recompression (Sumpton et al., 2010; Gitschlag and Renaud 1994; Collins et al., 1999; Jarvis and Lowe, 2008; Hannah et al. 2011). Additionally, CCFRP uses typical hook-and- line fishing gear in the recreational fishery, which may mean that barotrauma is less likely to occur in small fish because they rarely get caught on the bigger hooks.
Observations of release behavior at depth was effective for identifying rockfish with immediate behavioral impairment after capture. To ensure behavioral impairment was due to barotrauma injuries instead of being processed and descended, controlled rockfish without barotrauma injuries were also descended using the Barotrauma Reliever. Controlled rockfish that did not have barotrauma and were caught at similar depths as those with barotrauma, did not show behavioral impairment. Therefore, rockfish are behavioral impaired from the injuries of barotrauma, rather than being descended in the Barotrauma Reliever. Behavioral scores revealed differences between rockfish species in how effective recompression was at alleviating immediate behavioral impairments caused by barotrauma. When analyzing the video data of rockfish being descended via the
Barotrauma Reliever, Gopher Rockfish were the least behavioral impaired after
recompression. Behavioral impairment at release has been linked to predicting mortality in some species of fish (Davis 2005; Davis and Ottmar 2006, Rodgveller et al., 2017). Davis and Ottmar (2006) found loss of vertical orientation was a good indicator in subsequent mortality in Walleye Pollock (Theragra chalcogramma), Sablefish (Anoplopoma fimbria), Northern Rock Sole (Lepidopsetta polyxystra), and Pacific Halibut (Hippoglossus stenolepis). Therefore, Gopher Rockfish may have the lowest delayed mortality from barotrauma compared to Canary, Blue, and Deacon Rockfish.
It is unclear how long it takes barotrauma symptoms and behavioral impairments to be alleviated. I observed some symptoms dissipate during recompression, therefore some signs of barotrauma can subside within seconds of recompression. While, other signs of barotrauma persisted even after recompression. Based on my video data, I
observed everted esophageal tissue dissipate the most, while exophthalmia persisted the most.
Recovery from barotrauma can take hours to days, even with recompression (Rogers et al., 2001, Rodgveller et al., 2017). Sixty-nine of all the fish I recompressed did not display symptoms of barotrauma after recompression. After 2 days of recompression, Jarvis and Lowe (2008) saw less than 1% of rockfish still displaying barotrauma signs. Therefore, recompression appears to help decrease barotrauma symptoms (Hannah and Matteson, 2007; Hannah et al, 2011; Hochhalter and Reed, 2011; Jarvis and Lowe, 2008; Parker et al. 2006).
Rockfish can be behaviorally impaired from barotrauma even after they are recompressed (Jarvis and Lowe, 2008; Hannah et al. 2011, Rodgveller et al., 2017). For example, 26% of recompressed rockfish did not show external signs of barotrauma but did not swim away from the Barotrauma Reliever, instead they appeared stunned and drifted out of view from the camera. Some symptoms of barotrauma can have longer lasting effects (Rogers et al., 2011; Davis, 2005) than other symptoms. For example, corneal emphysema was shown to negatively affect the vision of Rosy Rockfish
(Sebastes rosaceus) a month after recompression (Rogers et al., 2011). Thus, the 31% of rockfish that still exhibited signs of barotrauma in my study may have needed more time for the symptoms to dissipate.
Recompressing fish has been shown to increase short-term survival (Curtis et al., 2015; Hannah et al., 2012; Jarvis and Lowe 2008, Rodgveller et al., 2017). Red snapper (Lutjanus campechanus) were more likely to survive barotrauma within a 72-hour period after release when recompressed to compared to vented surface release and nonvented
surface release (Curtis et al., 2015). Hannah et al., 2012 observed 78% of Blue Rockfish and 100% of Canary Rockfish were alive 41-71 hours after recompression from
barotrauma. Jarvis and Lowe (2008) found post recompression survival to be species- specific for rockfishes, with only 36% of Squarespot Rockfish (Sebastes hopkinsi) surviving 2 days after recompression from barotrauma, while 82% of Starry Rockfish (Sebastes constellatus) survived. This information further supports that rockfish species respond differently to recompression following barotrauma.
Two hundred thirty-nine rockfish were recaptured at depths between 18-33 m, between the years 2007 and 2015. The recaptured rockfish were of various species, with some exhibiting signs of barotrauma. Twenty of the 239 recaptures initially had
barotrauma when they were first caught. The recapture rate of all tagged rockfish was 0.437%, and the recapture rate of rockfish with barotrauma was 0.037%. The recapture rates are expected to be low due to the sampling protocol of CCFRP (Starr et al., 2015). The 20 recaptured rockfish that initially had barotrauma lived between 22 days and 3 years after having barotrauma (Table 10). This data shows that rockfish having barotrauma injuries are recaptured at a lower rate than rockfish not experiencing barotrauma. It is unknown if these rockfish were descended or not because it is not a required protocol for CCFRP. However, it does suggest rockfish can survive long term after experiencing barotrauma. Other studies have observed increased survivorship of fish experiencing barotrauma when they are recompressed (Hochhalter and Reed, 2011; Jarvis and Lowe, 2008; Parker et al. 2006). A seventeen-day mark and recapture study
analyzing the effectiveness of deep water release on Yelloweye Rockfish showed 98% survived after deep depth release, while only 22% survived when released at the surface
(Hochhalter and Reed, 2011). Ninety-seven percent of Black Rockfish (Sebastes
melanops) survived 21 days after experiencing barotrauma when they were recompressed in a pressure chamber (Parker et al., 2006). Jarvis and Lowe 2008 reported 3% of
rockfish initially having barotrauma were recaptured after deep depth release. Days at liberty for the recaptured fish was between 14-447 days (Jarvis and Lowe, 2008). All of this data further suggests rockfish can survive long-term after barotrauma if released at depth.
This information is pertinent for management implications because rockfish are not required to be descended. Thus, some anglers release unwanted fish at the surface because it is easiest, fastest, and cheapest (Hazell et al., 2016). This is an issue because rockfish are less likely to survive if they have barotrauma and are released at the surface (Hannah et al., 2008b; Hochhalter and Reed, 2011; Jarvis and Lowe, 2008; Parker et al. 2006). One study found 70% of Canary Rockfish and 68% of Blue Rockfish were unable to submerge themselves at the surface within 5 minutes when caught between 30-51 m (Hannah et al., 2008b). Therefore, a recompression device was properly used to recompress undesired fish it could help increase the survivorship of fish having barotrauma (Hannah and Matteson, 2007; Hannah et al, 2011; Hochhalter and Reed, 2011; Jarvis and Lowe, 2008; Parker et al. 2006).
The Barotrauma Reliever is an effective device––successfully transporting and releasing fish at a desired depth 84% of the time. Additionally, 69% rockfish were recompressed and did not exhibit any signs of barotrauma upon release. However, the device was unsuccessful in strong currents because it sank at an angle and usually did not reach the seafloor. It was also faulty when a small fish became stuck in one of the square
holes on the exterior of the crate because the fish could not swim out. These issues occurred 16% of the time. Simple adjustments such as decreasing the diameter of the holes on the crate would allow fish of all sizes to be descended. Adding weights during strong currents would correct the Barotrauma Reliever from drifting at an angle. With more testing and design improvements, the Barotrauma Reliever could become more effective.
Other descending devices are available to recompress fish as well. Hazell et al. (2016) analyzed the effectivity of several different descending devices for multiple species in the Mid-Atlantic and found that 64% of the devices were successful. Most importantly, 93% of anglers said they would support captains using descending devices (Hazell et al., 2016). However, in order to get support from all anglers, incentives such as extended fishing seasons or bag limits for captains regularly using descending devices were suggested by Sea Grant (Hazell et al., 2016). Therefore, using the Barotrauma Reliever is a practical technique in decreasing discard mortality. With the successes of the Barotrauma Reliever, it is economically and ecologically important to further
investigate and implement techniques to decrease discard mortality in rockfish. This work adds to the growing body of literature that suggests the need to recompress undesirable fish. This area of research needs more attention, especially since recompressing fish can potentially decrease discard mortality. Therefore, some fisheries could benefit from requiring undesirable fish to be descended. Descending fish gives the organism the opportunity to survive and reproduce, in turn creating more offspring to support the fishery. Continued research on recompression will help our understanding on how well fish survive after recompression.